linux-kernel - Re: [RFC] resource: Avoid unnecessary resource tree walking in __region

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <ZwkCt_ip5VOGWp4u@smile.fi.intel.com>
Date: Fri, 11 Oct 2024 13:49:27 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: "Huang, Ying" <ying.huang@...el.com>
Cc: David Hildenbrand <david@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, linux-cxl@...r.kernel.org,
	Dan Williams <dan.j.williams@...el.com>,
	Davidlohr Bueso <dave@...olabs.net>,
	Jonathan Cameron <jonathan.cameron@...wei.com>,
	Alistair Popple <apopple@...dia.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>, Baoquan He <bhe@...hat.com>,
	Dave Jiang <dave.jiang@...el.com>,
	Alison Schofield <alison.schofield@...el.com>
Subject: Re: [RFC] resource: Avoid unnecessary resource tree walking in
 __region_intersects()

On Fri, Oct 11, 2024 at 09:06:37AM +0800, Huang, Ying wrote:
> David Hildenbrand <david@...hat.com> writes:
> > On 10.10.24 08:55, Huang Ying wrote:

...

> > 	for ((_p) = (_root)->child; (_p); (_p) = next_resource_XXX(_root, _p))
> 
> Yes.  This can improve code readability.
> 
> A possible issue is that "_root" will be evaluated twice in above macro
> definition.  IMO, this should be avoided.

Ideally, yes. But how many for_each type of macros you see that really try hard
to achieve that? I believe we shouldn't worry right now about this and rely on
the fact that root is the given variable. Or do you have an example of what you
suggested in the other reply, i.e. where it's an evaluation of the heavy call?

> Do you have some idea about
> how to do that?  Something like below?
> 
> #define for_each_resource_XXX(_root, _p)                                \
> 	for (typeof(_root) __root = (_root), __p = (_p) = (__root)->child; \
> 	     __p && (_p); (_p) = next_resource_XXX(__root, _p))

This is a bit ugly :-( I would avoid ugliness as long as we have no problem to
solve (see above).

> > XXX TBD
> >
> > Or do you think this should not only be "improved" for the __region_intersects() use case
> > but for all for_each_resource() users? I cannot tell easily.
> 
> I prefer to make for_each_resource() to traverse only descendant
> resource tree of "_root".  This helps code reusing and make the
> interface easier to be understood.  The difficulty lies in twice
> evaluation as above.

-- 
With Best Regards,
Andy Shevchenko